During illumination of dark grown maize plants, the activities of phosphoenolpyruvate carboxylase in the mesophyll cytoplasm and malic enzyme in the bundle-sheath cell chloroplasts increase rapidly. These activity increases are the result of specific protein synthesis, for immunoprecipitable phosphoenolpyruvate carboxylase and malic enzyme protein increase during greening, and 35S-methionine is incorporated into these proteins. Cell-free translations of poly A+ RNA extracted over the course of greening indicate that translatable RNA for the two proteins accompanies the increase in activity and the increase in protein. We propose to study the processing of the precursor to malic enzyme synthesized in the cell-free traslation system. This precursor is much larger than expected on the basis of other cytoplasmically synthesized chloroplast proteins, and we will determine if it is processed in the same manner as others and if such processing is limited to bundle sheath chloroplasts. We are cloning ds cDNA prepared from total poly+ RNA of the light stimulated tissue in pBR 322, and we will use radiolabeled poly A+RNA fractions, enriched for phosphoenolpyruvate carboxylase and malic enzyme RNAs, to screen this clone bank for the specific complementary clones. The identity of such clones will be confirmed by hybrid selected translation of poly A+ RNA. We will use specific clones to quantitate the levels of mRNA for the two proteins in the leaf tissues during the greening period by solution hybridization. We will also determine the copy number of the genes for phosphoenolpyruvate carboxylase and malic enzyme in genomic DNA. Further, competition-hybridization experiments will be used to identify and quantitate the number of genes that become active on light stimulation of the dark grown plants.